The present invention relates generally to the tap art and concerns more particularly taps of the type in which the sealing action between the fluid inlet and the discharge is produced by a sealing joint provided on the tap head co-operating with a seat provided in the tap body.
In taps of this kind, when the seat, which is machined in the solid, is damaged and is no longer capable of effecting a seal, the repairer of the tap is faced with two solutions, either to grind the seat, or to incorporate a new seat into the body of the tap, after preparation of the tap body by successive machining operations.
The known state of the art is illustrated by U.S. Pat. No. 2,573,790 (H. Herzog) which describes apparatus, and the successive operations, for fitting a separate seat into the body of a tap, and by British Pat. No. 178684 (Taylor) which describes an apparatus for grinding a tap seat.
These prior apparatus which comprise three coaxial members (tool-carrier shaft, screw-threaded sleeve and adaptor) overcome the disadvantage of unacceptable insufficiency in respect of the guiding action, as the assembly rapidly suffers from play which detrimentally affects the quality of the seat produced.
In the above-quoted British patent, the apparatus described also suffers from the serious disadvantage that, without an axial restraint means, if the operator applies to the tool-carrier shaft a thrust force which is only a little higher than a threshold value compatible with the material to be machined, the tool `bites` into the seat, producing imprints which it is then difficult or even impossible to remove.
Finally, the quality of the truing operation often leaves much to be desired by virtue of a limitation in regard to the amount of material which can be removed at a time without the danger of choking the tool, and by virtue also of an imperfect surface condition of the seat.